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Isocyanate-Free Polyurethane Maker Glosses Over Bisphenol-A Content

A cement floor before treatment with Green Polyurethane.

A new clear floor coating for the commercial and industrial market is being touted as not containing isocyanates, potentially toxic chemicals used in uncured spray polyurethane foams (SPF), clear furniture and floor coatings, and adhesives such as those found in no-added-formaldehyde wood panel products. But it does contain epoxy, made from bisphenol-A. Can an epoxy-based polyurethane truly be "green" as its name attests?


Green Polyurethane from Nanotech Industries International, Inc. is a hybrid polyurethane that uses a proprietary combination of epoxy and polyurethane technologies that, according to the company, creates a surface that has better adhesion, three to four times the corrosion resistance, and 50% more chemical resistance than conventional polyurethanes. And it does so without solvents, VOCs, or the use of isocyanates. Sounds great! Unfortunately, epoxy is made from the endocrine disruptor bisphenol-A (BPA).

Isocyanates and onsite emissions

Isocyanates are a class of common industrial chemicals that include methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI), and hexamethylene diisocyanate (HDI).

You might have heard more about them since the EPA recently announced an action plan for MDI and related chemicals that requires U.S. companies to report information if one of their chemicals "presents a substantial risk of injury to health or the environment."

Isocyanates are toxic during application where the emissions can irritate eyes, nose, throat, and skin; and cause asthma and other health problems. But, once the polyurethane is fully cured, risk of exposure to occupants appears limited.

A substitute for some applications

The chemistry behind Green Polyurethane is complex. Nanotech Industries International's senior technical advisor Peter Gulko calls it a network polymer, where two different materials intertwine and become inseparable, yet there is no chemical bond between them. In this case the combination of epoxy and proprietary isocyanate-free polyurethane form a "nano" structure that is not porous or permeable.

Leon Zigelman of Mallet Millwork Inc in Toronto is impressed by its strength. He said he applied Green Polyurethane over concrete at a 1 mm thickness, as compared to nearly ¼ inch for a standard epoxy, and had people try to chip it with a hammer. According to Zigelman, the concrete chipped first.
 

A cement floor after treatment with Green Polyurethane.

Nanotech Industries is marketing Green Polyurethane to cement applications in high-traffic areas or where chemical resistance is required. In these applications a primer, an epoxy layer, and a polyurethane topcoat for abrasion resistance are typically used, but Green Polyurethane doesn't need the epoxy layer, is stronger than polyurethane, and, depending on the substrate, may not need a primer, according to the company.

Substituting one toxic material for another

Gulko says we shouldn't worry about the BPA in Green Polyurethane. He claims it is fully bonded within the polyurethane so it shouldn't offgas or leach out. But there is some evidence that the byproducts of BPA during application can be metabolized by the body back into BPA. Whether or not this process happens with Green Polyurethane's formula is unclear, but the product poses a challenge for us here at GreenSpec.

In cases of unknown chemistries we often invoke the precautionary principle, choosing not to list products where there may be reasonable question of their long-term health or environmental impact. Green Polyurethane's isocyanate-free formula might provide protection for concrete flooring and could have a niche in reducing the amount of epoxy used in specialized applications, but Nanotech Industries touts the environmental advantages of being isocyanate-free while never mentioning BPA in its literature.

You have to dig down into the MSDS for that information. GreenSpec encourages the development of isocyanate-free polyurethanes (we list Vermont Natural Coatings isocyanate-free whey-protein polyurethanes for wood applications, for example), but we are not convinced that using epoxy is the best substitute.
 

 

Brent Ehrlich is the products editor at BuildingGreen, Inc.

Posted by Brent Ehrlich on May 25, 2011

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